Originally Posted by Finley Atherton
Fourteen years ago I tested this with a dead engine and the prop would go coarse just like if the engine was idling. Hartzell, MT governor, O-320.
At 70 kts with the mixture at idle cut off (dead engine) and the prop control full out (coarse):
Oil pressure 50 psi
Yes, I’ve had similar results with true power-off glide tests. My MT governor on my IO-360A1B6 will govern to a low enough speed that it will cycle the prop to full coarse pitch when cranking the engine with the starter and the upper plugs pulled out! In actual glide tests with the mixture pulled to ICO, the governor has no problem governing the prop down to 600 RPM or so. This was tested through about 2000’ of glide, multiple times. If the prop is windmilling the oil pump is pumping. Now as posted above, if the engine failure is the result of a catastrophic internal failure that causes a loss of oil pressure, the governor will not work so this option might not be available in a real emergency.
Also, the windmilling RPM of the engine is dependent on the actual glide airspeed.